Optically active 2,2′-biphenol derivatives are important compounds as synthetic intermediates of ligands for asymmetric synthesis of various fine chemicals consisting primarily of pharmaceuticals and agrichemicals.
A known example of such a 2,2′-biphenol derivative is a 6,6′-disubstituted-2,2′-biphenol derivative represented by the following formula (A)
(wherein, Ra represents an optionally substituted lower alkyl group, and * represents an axially asymmetric center).
Known examples of methods for obtaining an optically active 2,2′-biphenol derivative represented by the aforementioned formula (A) include a method in which a meso form of biphenyl is converted to an optically active compound followed by deriving to optically active 2,2′-biphenol, and a method in which a racemic form of 2,2′-biphenol is converted to a diastereomeric mixture followed by optical resolution.
Methods for producing meso and racemic forms of biphenols typically use oxidative ortho-coupling of a substituted resorcinol or substituted phenol by potassium hexacyanoferrate(III)(potassium ferricyanide), di-t-butyl peroxide, ferric chloride or oxygen and the like.
As an example of a method for converting a meso form of biphenyl to an optically active compound followed by deriving to optically active 2,2′-biphenol, a method is reported in Non-Patent Document 1 in which 2,2′,6,6′-tetrahydrobiphenyl is converted to an acetal derivative of optically active menthone followed by deriving to an optically active 6,6′-disubstituted-2,2′-biphenol.
Examples of methods for converting a racemic form of 2,2′-biphenol to a diastereomeric mixture followed by optical resolution include a method in which a phosphoric acid derivative of a racemic form of 6,6′-disubstituted-2,2′-biphenol is esterified by reacting with optically active menthol followed by optical resolution (Patent Document 1), and a method in which only one of the optical isomers of a racemic form of 6,6′-disubstituted-2,2′-biphenol is selectively crystallized with optically active cyclohexanediamine (Patent Document 2).
However, the methods described in Non-Patent Document 1 and Patent Document 1 have a complex procedure due to the need for a multistage synthesis route, while the method of Patent Document 2 has the problem of low reaction yield.
In addition, although a method is known for synthesizing a racemic form of 3,3′,6,6′-tetraalkyl-5,5′-dihalogeno-2,2′-biphenol (Patent Document 3), there is no description of a method for producing optical isomers.
On the other hand, optically active 2,2′-biphenol derivatives represented by the following formulas (B) and (C):
(wherein, * is the same as previously defined) are useful as precursors of asymmetric phase-transfer catalysts.
However, since both of these compounds are synthesized from optically active 6,6′-dimethyl-2,2′-biphenol represented by the aforementioned formula (A) (Non-Patent Document 2), they have the same problems as the previously described production methods.    [Patent Document 1] Japanese Unexamined Patent Application, First Publication No. 2004-189696    [Patent Document 2] Japanese Unexamined Patent Application, First Publication No. H10-45648    [Patent Document 3] Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2005-510551    [Non-Patent Document 1] SYNLETT, 1995, No. 3, 283-284    [Non-Patent Document 2] Organic Process Research & Development, Vol. 11, pp 628-632, 2007